Selecting the Right Drive System – Cost and Performance

When making a drive conversion or designing a new power transmission system, plant maintenance and design engineers have basically three broad options:

• Roller chain drives
• V-belt drives
• Synchronous belt drives

Each has its own advantages and disadvantages, along with cost considerations that may not be immediately apparent.

Roller Chain Drives

Gates Drive System

The popularity of chain drives stem from the ability of these drives to transmit high torque levels in a small package, at relatively low cost, while utilizing readily available stock components. While initial costs of standard roller chain drives might be quite low, the cost of maintaining these drives can be substantial. Proper maintenance is essential for optimal roller chain drive performance, and includes the following cost factors:

• Lubrication
• Alignment
• Tension
• Drive component replacement

According to chain industry estimates, roller chain drives operating without lubrication wear approximately 300 times faster than comparable drives that are properly lubricated. And yet, roller chain manufacturers estimate that 90 to 95% of all installed drives are either improperly lubricated, or not lubricated at all. Determine the type of lubrication method needed is a major design consideration with cost implications of its own. An oil retaining chain housing, for example, can represent up to 75% of total chain drive system cost. In addition to lubrication, proper sprocket alignment and chain tensioning are critical to increasing roller chain life.

Another maintenance factor with cost implications is drive component replacement. One of the major weaknesses of a roller chain drive is chain wear resulting in stretching or elongation. Manufacturers recommend roller chain replacement when elongation of approximately 3% has occurred. Most roller chain manufacturers also recommend replacing sprockets with each new roller chain, because the metal-to-metal contact generates severe sprocket wear. Power rating tables published within the roller cahin industry are based on a theoretical design life of 15,000 hours, assuming proper drive design, alignment, lubrication, maintenance, etc., but in a typical operating environment, actual drive life rarely approaches the ideal. Unlubricated roller chain drives operating under harsh conditions can be as short lived as 100 hours or less.

The cost of the maintenance requirements noted above, added to the initial cost, approximates the true cost of a standard roller chain drive, However, beyond the cost of lubricant and drive component replacement is the labour expense of frequent re-tensioning, which requires shutting down the drive, resulting in production downtime. Also, standard roller chain drives operate at 91%-94% efficiency, depending on the application, so energy costs must be taking into account.

Maintenance and energy costs notwithstanding, roller chain drives offer designers and users some advantages over V-belt or synchronous belt drive systems:

1. Versatility (functional attachments can be added to convey products, trip switches, actuate levers, etc.)

2. Ability to create any length of chain with connecting links

3. Availability of large selection of chain and sprockets

V-Belt Drives

V-belt drives transmit power through friction between the belt and pulley. With efficiencies ranging from 95% to 98% at installation, V-Belt drives use energy more efficiently than roller chain drives, and somewhat less efficiently than synchronous belt drives. V-belt drives are an industry standard, offering a wide range of sizes at relatively low cost, along with ease of installatino and quiet operation.

V-belts are manufactured in a variety of materials, cross-sections and reinforcement materials, and are often used singly, in matched sets or in joined configurations. They are well sutied for severe duty applications, such as thous involving shock loads and high starting loads. Standard V-belt drives operate best in appliactions of 500 RPM or greater, speed rations of up to 6:1, and within a limited operating temperature range of -40 Fahrenheit to 130 Fahrenheit. Because V-belts slop when overloaded, they help protect more expensive equipment from load surges. They also allow flexibility in the positioning of the motor and the load.

In a suitable application, the service life of a properly installed and maintained V-belt drive ranges form 20,000 to 25,000 hours. The components of a simple V-belt drive are relatively inexpensive to purchase, install, replace and maintain. After they are installed properly and tensioned to the belt manufacturer’s recommended values, these drives require very little servicve, except for re-tensioning during the normal maintenance schedule. Due to belt slippage, V-belt drives lose up to 5% of their efficiency after installation. V-belts stretch as they wear, making slippage worse, which can decrease efficiency as much as 10& unless by periodic re-tensioning. Cogged or notched V-belts can increase efficiency by 2% over standard designs.

Synchronous Belt Drives

Synchronous belts work on the tooth-grip principle. Round, square or modified curvilinear belt teeth mesh with grooves on sprockets to provide positive power transmission on high-torque with high and low speeds.

The components of a synchronous belt drive system typically cost more initially than those of a comparable standard roller chain drive or V-belt drive. By contrast, synchronous belt drives do not have the maintenance cost associated with roller chain drives. They require no lubrication and thus no lubrication system, only basic safety guarding. While roller chain requires frequent re-tensioning, and V-belts required periodic re-tensioning, a synchronous belt typically requires no re-tensioning for the life of the belt.

To illustrate the amount of elongation that can occur in a roller chain, recommended centre distance take up allowances for belt drives can be compared to centre distance take up needed for a roller chain in the same length. Assuming a length of 100 inches, a roller chain, V-belt and synchronous belt can be compared as follows:

Roller Chain – Roller chain will elongate about 3″ (or 3%) over its life, requiring about 1.5″ of centre distance take up.

V-Belt – A V-belt requires 1.5″ to 2.5″ of centre distance take up over its life, depending upon the cross section and manufacturer.

Synchronous Belt – A synchronous belt typically requires only .04″ of centre distance take up over its life, depending upon the belt type and manufacturer.

Chain and sprocket wear are significant cost factors in a roller chain drive. Synchronous belts and sprockets experience dramatically less wear. In a Gates Poly Chain GT2 drive system, for example, the belt will outlast a comparable roller chain on the order of 3 to 1, and the sprockets will outlast roller chain sprockets 10 to 1.

Like roller chain drives, synchronous belt drives are sensitive to misalignment and should no be used on systems where it is inherent to the drive operation. Misalignment leads to inconsistent belt wear and premature tensile failure due to unequal tensile member loading. And while a synchronous belt like Poly Chain GT2 is resistant to abrasion, corrosion and the caustics wash-down solutions used in the food handling/processing industry, it may not be suitable for certain highly corrosive environments where corrosion resistance chain may be a better alternative.

One misconception about synchronous belts is that hey are unsuitable for serpentine drives. Design engineers may think that roller chain is the only option when a load must be driven off both sides; however, double-sided synchronous rubber belts like Gates PowerGrip GT2 Twin Power offer many of the same cost-savings advantages over roller chain as their single-sided cousins. Due to their high efficiency ratings (as high as 99% on a continuous basis in a Poly Chain GT2 drive system), synchronous belt drives can also lower energy costs compared with roller chain drives, which typically operate at 91-94% efficiency, or V-belt drives, which when properly tensioned, operate at 93-95% efficiency.

Conclusion

When considered on a cost-of-ownership basis, a synchronous belt drive system can be more cost-effective than a comparable roller chain drive or V-belt drive system. A Gates Poly Chain GT2 belt drive (incorporating the most technically advanced synchronous belt available, made of a polyurethane body and aramid fiber reinforcement), for example, initially costs an average of 30% more than a comparable standard roller chain drive. However, it has many cost-savings advantages for plan maintenance managers and design engineers.

In the MRO market, synchronous drives can greatly reduce day-to-day operational costs, and increase production output compared to the downtime and lost productivity resulting from all-too-frequent maintenance and replacement of roller chain and V-belt drives. Drive system design engineers who select a synchronous drive, such as the Gates Poly Chain GT2 belt system, can give their products a competitive edge in the marketplace by providing end-user customers with better performing, longer lasting, cleaner, quieter, and maintenance free products that will operate at significantly lower overall cost.

At J/E, we are an authorized distributor for Gates. We carry products such as belts, hoses and sprockets. To inquiry about any of our products head on over to our contact page or email us at info@je-bearing.com